Digital Subscriber Line (DSL) technology is widely-used today for increasing the bandwidth of digital data transmissions over the existing telephone network infrastructure. In a typical system configuration, a number of DSL subscribers are connected to a service provider (SP) network through a Digital Subscriber Line Access Multiplexer (DSLAM), which concentrates and multiplexes signals at the telephone service provider location to the broader wide area network. DSL network operators are increasingly deploying DSLAMs that act as Layer 2 (L2) Ethernet access nodes.
One of the functions attributed to these devices is that of being able to perform IP multicast traffic replication at L2 using standard Internet Group Management Protocol (IGMP) snooping behavior. (IGMP is a well known Internet protocol that provides a way for a computer to report its multicast group membership to adjacent routers. IGMP snooping is an attribute of Ethernet L2 devices that perform multicast replication control. Multicasting is a technique that allows one computer on the Internet to send content to multiple other computers that have identified themselves as interested in receiving the originating computer's content.) Essentially, the DSLAM snoops (i.e., captures and analyzes) IGMP messages sourced by directly attached subscribers and creates or removes multicast L2 forwarding entries accordingly. Network operators use multicast traffic replication at the DSLAM access node to optimize the use of bandwidth resources in the aggregation network while still delivering multicast services to multiple subscribers attached directly to the access node.